Joining Hagar on the charity concert line-up are country music legends Mel Tillis and John Anderson.

"When Toby asked me to come on board, I immediately said yes," Hagar said in a statement. "He's put together a hell of a concert lineup to help raise funds for the brave and resilient people of Oklahoma.

"My job is going to be to help them take their minds off their problems and have some much-needed, good old-fashioned fun."

Keith previously announced that Garth Brooks, Willie Nelson and Trisha Yearwood will also appear at his benefit. Tickets go on sale on Friday (June 21).

The 'Oklahoma Twister Relief Concert' is being held at the University of Oklahoma's Gaylord Family-Oklahoma Memorial Stadium.

A separate tornado relief concert will be headlined by Kings of Leon, The Flaming Lips and Jackson Browne on July 23 in Oklahoma City.